Polyamides are an important and well known class of polymers used as fibers (textile and industrial) as well as in construction and are formed by the condensation polymerization of a diamine and a diacid chloride. Poly(hexamethylene adipamide) was the first synthetic fiber produced industrially on a large scale by Carothers with the trade name nylon-66 and it has the following structure. EQU H--(--NH--(CH.sub.2).sub.6 --NH--CO--(CH.sub.2).sub.4 --CO--(.sub.n --OH
Nylon-66 is one of the important polyamides with an excellent fiber and thermoplastic properties. For example, nylon-66 is silk like and has displaced both natural silk and cotton from the market. In addition, it can be readily dyed or pigmented and has good texturizing properties. The dyeability can be varied within wide limits by copolymerization with monomers containing acidic or basic groups, by end group variation, or by grafting. Such applications in various areas other than the textile industry has also been very well documented in literature. Polyamides containing aliphatic cyclic structures in the polymer chain are somewhat superior to the acyclic polyamides in terms of thermal stability, whereas aromatic polyamides have greatly improved thermal stability compared to aliphatic polyamides. However, most of these polyamides are soluble only in H.sub.2 SO.sub.4, formic acid and m-cresol. Thus, the net range of studies of these polymers in solution is limited.
An object of the present invention is to utilize open chain Reissert chemistry to improve the properties of polyamides. U.S. Pat. No. 4,929,713 reports the synthesis of open chain poly(Reissert compounds) by the aromatic dialdehyde and primary amine, in the presence of cyanide and bisulfite, followed by reaction of the product with an aliphatic diacid chloride. It does not suggest use of Reissert chemistry for the modification of polyamides.